The present invention relates to servo information recording technology. More particularly, it relates to techniques which are effective when applied to the operation of recording servo tracks in the manufacturing process of magnetic disks, and a magnetic disk apparatus which utilizes the techniques.
In a magnetic disk apparatus, a plurality of magnetic disks held coaxial are rotated. The recording surface of each of the magnetic disks is provided with a plurality of concentric tracks which are regions for recording information. A magnetic head which is disposed in opposition to the recording surface of the corresponding magnetic disk, is displaced radially of this magnetic disk so as to be located on a target track. Thereafter, the magnetic head records/reproduces information on/from the target region of the recording surface. As a method for positioning the magnetic head onto the target track, it is known to record servo information on the recording surface of the magnetic disk beforehand and to use the servo information for the positioning.
With this method, the recording surface of one of a plurality of magnetic disks set is utilized. A specified servo pattern is concentrically recorded on the recording surface in advance. In case of, for example, a two-phase servo system, the servo pattern defines four servo regions S.sub.1, S.sub.2, S.sub.3 and S.sub.4 as regions for writing signals. A first position signal is generated by comparing the magnitudes of the signals of the regions S.sub.1 and S.sub.3 among the four servo regions, while a second position signal is generated by comparing the magnitudes of the signals of the regions S.sub.2 and S.sub.4. Subsequently, the servo information is obtained from the first and second position signals (in two phases).
A technique for writing such a servo pattern is disclosed in the official gazette of Japanese Patent Application Publication No. 64812/1988. In writing the servo pattern, this technique employs a magnetic head having a core width which is not smaller than the product between the width of a track and the number of phases of the servo pattern. After having erased a target track in one predetermined direction with D.C. beforehand, the magnetic head causes a current opposite in sense to the erasing D.C. to flow through the designated region of the track so as to write the servo pattern. The magnetic head writes on and on through this operation while repeating its advances and retreats in the radial direction of tracks.
On the other hand, a technique for reading out a written servo pattern and verifying write signals is disclosed in the official gazette of Japanese Utility Model Registration Application Laid-open No. 105967/1988. With this technique, the same magnetic head as one having written the servo pattern is used for reading and verifying this servo pattern.